TM 10-1670-299-20&PTO 14D1-2-470-2NAVAIR 13-1-41C-3. EXPLANATION OF COLUMNS. (Sections II and III). (CONT)XDItem is not stocked. Order an "XD" - coded item through normal supply channels using the CAGEC and part number given, if no NSN is available.NOTECannibalization or controlled exchange, when authorized, may be used as a source of supply foritems with the above source codes, except for those source coded "XA" or those aircraft supportitems restricted by requirements of AR 700-42.(2) MaintenanceCode. Maintenance codes tell you the level(s) of maintenance authorized to USE andREPAIR support items. The maintenance codes are entered in the third and fourth positions of the SMR Code asfollows:(a) The maintenance code entered in the third position tells you the lowest maintenance level authorized toremove, replace, and use the support item. The maintenance code entered in the third position will indicate authorizationto one of the following levels of maintenance:CodeApplication/ExplanationCCrew or operator maintenance done within unit or aviation unit maintenance.OUnit or aviation unit category can remove, replace, and use the item.FDirect support or aviation intermediate level can remove, replace, and use theitem.H General support level can remove, replace, and use the item.LSpecialized repair activity can remove, replace, and use the item.DDepot level can remove, replace, and use the item.C-4